20 Apr 2017

Read Time : 10 Minutes

In an ideal differential amplifier, differential voltage gain (Ad) is infinite while common mode voltage gain (AC) must be zero. However, in a practical differential amplifier; Ad is very large and AC is very small. ie., the differential amplifier provides very large amplification for difference signals and very small amplification for common mode signals. Many disturbance signals/noise signals appear as a common input signal to both the input terminals of the differential amplifier. Such a common signal should be rejected by the differential amplifier. “The ability of a differential amplifier to reject a common-mode signal is expressed by a ration called Common Mode Rejection Ratio, denoted as CMRR”. CMRR is defined as the ratio of the differential voltage gain Ad to common mode voltage gain AC.